Oil burner control



J. E. WILDER OIL BURNER CONTROL May 19, 1959 Filed July 25, 1956 FIG. 2

INVENTOR.

JUSTIN E. WILDER ATTORNEY United States Patent OIL BURNER CONTROL Justin E. Wilder, Goshen, Ind., assignor to Penn Controls Incorporated, Goshen, Ind., a corporation of Indiana Application July 25, 1956, Serial No. 600,008

Claims. (Cl. 158-28) Tlhis invention relates generally to oil burner controls and in particular to circuits for oil burner controls which utilize a combustion responsive thermostatwhich can be mounted in the conventional manner, unitary with the other circuit components, or can be mounted remotely from the control panel without establishing an unsafe condition upon any type of failure of the combustion responsive thermostat or any short-circuiting combination of the leads to the combustion responsive thermostat.

Oil burner circuits have been developed which can be used with remotely mounted combustion thermostats and which fail safe in that any short-circuiting or opening of the leads to the combustion thermostat results in a safe condition for the burner. An example of such a circuit is that of Schell Patent 2,743,768. In providing this fail-safe feature the circuit of the above mentioned patent requires the use of a thermal electric timing switch mechanism in which two sets of contacts must overlap in operation, i.e., one set of normally open contacts must close before the other set of normally closed contacts open to terminate the burner starting interval. Use of such overlapping contacts involves various difiiculties, among them assuring that the proper sequence of operation of the two sets of contacts is maintained, which normally requires close adjustment of the contacts and consequent calibration expense.

An object of the present invention is to provide an oil burner control circuit which can safely utilize a remotely mounted combustion responsive element and yet requires no overlapping contact arrangement of the switching portion of the circuit. r A further object of the present invention is to provide an oil burner control circuit having the feature of postignition (ignition timing does not start until combustion hasbeen established) and yet does not require the use of overlapping contacts in the customary thermal electric timing switch mechanism.

A further object is to provide an oil burner control circuit providing for checking the operation of the safety switch with each on-ofr" cycle of the burner without the use of overlapping contacts in the ignition timer switch mechanism or the combustion responsive thermostat.

These and other objects will be apparent from the following description of the invention, the preferred embodiment of which is shown in the drawings in which:

Figure 1 is a schematic illustration of the circuit in standby condition.

Figure 2 is a schematic illustration of the circuit in energized condition and the burner in operation.

Referring initially to Figure 1 there is shown at and 11 electrical power input lines having connected thereacross the primary coil 13 of a stepdown transformer 14. An oil burner motor 16 is connected aoross the wires 10 and 11 through a switch 17. Switch 17 also controls a circuit through an igniter 18 by means of wire 19, switch 21, and wire 22.

ice

A center tapped secondary coil 24 of the transformer 14 has connected to one of its ends a wire 25 which in turn is connected to one terminal of a conventional thermal electric type safety switch identified by reference numeral 26. Safety switch 26 includes a pair of normally closed contacts 27 and 28 and a bimetal operator 29 which holds the safety switch contact closed until the operator 29 warps from under the switch arms to permit the contacts to open. A reset button 34 permits resetting of the latching arrangement of the bimetal operator and contacts when the birnetal operator has cooled to its normal position. This safety switch is of conventional type and forms no part of the present invention. The other terminal of the safety switch has connected thereto a wire 35 which in turn is connected to one terminal of a switch 37 operated by an enclosure or room temperature responsive thermostat, the switch and its operator hereafter being referred to as a room thermosta or as an enclosure temperature responsive switch. The other terminal of thermostat 37 is connected to an electromagnetically operated relay coil 38 by means of a wire 39. The other side of relay coil 38 is connected to one side of a thermal electric warp element operated switch r 41 by means of a Wire 42. The other side of switch 41 is connected by wire 43 to a wire 44 which in turn is connected to a heater element 45 adapted to operate, upon heating, the bimetal latch member 29. The other side of heater 45 is connected by means of wire 47 to the closed cold contact 48 of a switch 49 operated by a combustion responsive thermostat hereafter referred to collectively as a combustion responsive thermostat. The common terminal of the combustion thermostat 49 is connected by means of a wire 51 to the other side of transformer secondary 24.

Wire 42 is additionally connected to a relay operated switch 52 by means of a wire 53. The other side 'of switch 52 is connected to a resistor 54 by means of wire 55. Resistor 54 is in turn connected to warp element heater 57 which, in turn, is connected to a closed hot contact 58 of the combustion thermostat 49 bymeans of wire 59.

A center tap 61 on transformer secondary 24 is connected by means of wire 62 to one side of a relay operated switch 63. The other side of switch 63 is connected to the junction of wires 43 and 44 by means of a wire 64. Connected in parallel with resistor 54, by means of wire .66 and 67 is a thermal electric warp element operated switch 68. Reference numeral 70 designates a bimetal operator for switches 41., 68, and 21, operator 70 being heated to operate the aforementioned switches by the heater 57. The warp element 70 and its accompanying heater 57 are of a conventional type and in themselves form no part of the present invention.

Operation When room thermostat 37 closes indicating a need for operation of the burner 16, relay coil 38 will be initially energized through a circuit extending from the top extremity of transformer secondary 24, wire 25, safety switch 26, wire 35, thermostat 37, wire 39, relay coil 38, wire 42, switch 41, wire 43, wire 44, safety switch heater 45, wire 47, contacts 48 of the combustion responsive thermostat 49, and via wire 51 back to the transformer secondary 24. Energization of relay coil 38 closes switches 52, 63, and 17 Closure of switch 17 starts operation of the burner motor 16, which thereupon supplies oil and air for combustion, and igniting means 18v 5 8 of the combustion responsive thermostat Closure of switch 63 provides a safety switch actuator circuitfor 3 safety switch heater 45, which is independent of the relay energizing circuit, as follows: from transformer center-tap 61, wire 62, switch 63, wire 64, wire 44, safety switch heater 45, contacts 48 of the combustion responsive thermostat 49, and via wire 51 back to the lower end of transformer secondary 24.

Within a short time after the establishment of combustion at the burner, combustion thermostat contacts 48 will open and. contacts 58 will close. Opening of contacts 48 breaks the safety switch actuator circuit which thereupon permits safety switch heater 45 to cool allowing bimetal latching member 29 to retain safety switch contacts 26 in closed position. Relay coil 38 will remain energized during the interval in which combustion thermostat 49 is opening contacts 48 and closing contacts'58 by means of a relay holding circuit which may be traced as follows: the top of secondary 24, wire 25, contacts 26, wire 35, thermostat 37, wire 39, relay coil 38, wire 42, warp switch 41, wire 43, wire 64, relay operated switch 63, wire 62 back to transformer tap 61.

Closure of combustion responsive contacts 58 establishes an ignition switch actuator circuit for energizing the warp switch heater 57 which may be traced from the junction of wires 42 and 53, the now closed relay switch 52, wire 55, wire 66, warp switch 68, wire 67, heater 57, and via wire 59 to the now closed contacts 58 of combustion responsive thermostat 49. Warp switch heater 57 thereupon begins to heat the bimetal element 70, warping it in a direction to presently open ignition switch 21, warp switch 68, and warp switch 41. It will be noted that these switches need not be opened in any particular sequence and may all open simultaneously or in any sequence over a short time interval.

Opening of warp switch 41 breaks the previously traced relay holding circuit and relay coil 38 and Warp switch heater 57 are retained energized, in series, by a circuit which may be traced as follows: from the top of secondary 24, wire 25, safety switch contacts 27-48, wire 35, thermostat 37, wire 39, relay coil 38, wire 53, relay switch 52, wire 55, resistance 54, warp switch actuator 57, wire 59, closed hot combustion contacts 58, and via wire 51 back to secondary 24. It will be noted that resistance 54 is placed in series with warp switch actuator 57 by the opening of switch 68. Resistance 54 performs the function of inserting additional resistance in the running circuit to cause relay 38 to drop out more readily on a partial loss of voltage at the energizing source. In general, resistance 54 and its shunting switch 68 do not form a part of the present invention, since if, in a particular application, sensitivity to voltage drops on the part of relay 38 were not a requirement, the presence of resistance 54 and its switch 68 would not be necessary.

()peration of burner 16 will continue by means of the continued energization of the last traced circuit until thermostat 37 is satisfied and thereupon opens its contacts.

Upon a combustion failure, or extinction of the burner flame during an on-period, combustion contacts 58 will open deenergizing warp switch actuator 57 and relay 38 thereby stopping the burner. Although combustion contacts 4-8 are immediately closed, reenergization of relay 38 will not take place until a purge period has passed, the duration of the purge period being timed by the cool ing' of warp switch actuator 57, since until warp switch 41 is reclosecl by such cooling, theinitial starting circuit cannot be reconstituted. After switch 41 recloses, the cycle will be restarted and if combustion is again establishednormal operation will continue. If combustion is not established, as evidenced by failure of combustion responsive thermostat 49 to move to its hot positionopening contacts 48, then safety switch heater 45 will remain energized and will after a short time cause .bimetal element29 to move out of latching engagement with'the contact assembly for safety switch contacts 27 and 28, permitting them to open shutting down the burner until the safety switch; contacts are reclosed by means of the 4. manual operator 34, after the cause of the burner malfunction has been eliminated.

In the event of ignition failure, or failure of the burner to ignite at the start of a cycle, operation and lockout throughout the safety switch will take place as just previously described.

Assuming combustion responsive thermostat 49 is located remotely from the other circuit components, which may be mounted on a control panel, the wires 59, 47, and 51 will be relatively long lead wires which will be subject to possible damage causing shorting or opening of any two or all three of the wires. In the presentcircuit no combination of open or shorted wires can result in an unsafe condition at the burner. If either of Wires 47 or 51 are open, the relay coil 38 cannot initially pull in. If wire 59 is open, the warp switch actuator 57 cannot be energized to open ignition switch 21 and the burner and igniter will be operated as a continuous ignition burner system with combustion responsive contacts 48 and safety switch heater 45 guarding against combustion or ignition failure. If wires 51 and 47 are shorted together, an energizing circuit for safety switch heater '45 will be maintained through the short to open the safety switch contacts 27 and 28 to shut down the burner. If

wires 59 and 51 are shorted together, the warp switch actuator 57 will be immediately energized upon closureof the thermostat 37, however, operation of the burner will proceed normally except that the ignition period (the' period from the start of the burner until ignition switch 21 is opened) will be foreshortened, and oncombustion failure a somewhat delayed lockout of the safety switch will occur rather than a recycling operation as previously described with reference to the normal circuit reaction to a combustion failure.

From the foregoing it will be apparent that the described circuit provides for safely mounting the combustion responsive thermostat remotely from the other con1- ponents and accomplishes its operational sequence without use of overlapping or sequential combustion responsive switches or warp switches.

Modifications of the present invention may occur to those skilled in the art without departing from its scope, which is to be limited only by the appended claims.

What is claimed is:

1. A control circuit for a fluid fuel burner for heating an enclosure of the type in which a main burner switch controls the flow of fuel to the burner and an ignitionswitch controls energization of the ignition means for the fuel, said circuit comprising: a transformer having a secondary winding serving as a source of power for the control circuit; a combustion responsive thermostat having a first setof contacts closed in the absence of conn bustion and a second set of contacts closed in the presence of combustion, a safety switch actuator circuit and an ignition switch actuator circuit connected in parallel across said secondary winding and controlling energization of an electric safety switch actuator and anelectric ignition switch actuator respectively, said'safety switchactuator circuitcomprising: a normally closed switch opened by said ignition switch actuator a predetermined time after its energization, a thermal electric safety switch actuator, and said first set of contacts of said combustion responsive thermostat; said ignition switch actuator circuit comprising: a normally open ignition switch actuator'control switch, an ignitionswitch actuator, and said second set of contacts of said combustion responsive thermostat; wiring means including a normally open safety switch actuator holding switch connecting an intermediate tap on'said transformer secondary with said safety switch actuator circuit at the junction of said normally closed switch and said safety switch actuator; an electrical main burner switch operator adapted when energized to closeboth said ignition switch actuator control switchand said safety switch actuator holdingswitch; said main burner switch operator, a normally closed safety switch operated by said safety switch actuator, and an enclosure temperature responsive switch being serially connected between said transformer secondary and said safety and ignition switch actuator circuits.

2. A control circuit for a fluid fuel burner for heating an enclosure of the type in which a main burner switch controls the flow of fuel to the burner and an ignition switch controls energization of the ignition means for the fuel, said circuit comprising: a transformer having a secondary winding serving as a source of power for the control circuit, a combustion responsive thermostat having an element adapted to respond to the heat of combustion at the burner and adapted to operate a first set of contacts whichare closed in the absence of combustion. at said burner and a second set of contacts which are closed in the presence of combustion at said burner, a safety switch actuator circuit and an ignition switch actuator circuit connected in parallel across said secondary winding and controlling energization of an electric safety switch actuator and an electric ignition switch actuator respectively, said safety switch actuator circuit comprising: serially connected a normally closed switch opened by said ignition switch actuator a predetermined time after its energization, a safety switch actuator, said first set of contacts of said combustion responsive thermostat; said ignition switch actuator circuit comprising: serially connected a normally open ignition switch actuator control switch, an ignition switch actuator, and said second set of contacts of said combustion responsive thermostat; wiring means including a normally open safety switch actuator holding switch connecting an intermediate tap on said transformer secondary with said safety switch actuator circuit actuator; an electrical main burner switch operator adapted when energized to close both said ignition switch actuator control switch and said safety switch actuator holding switch; said main burner switch operator, a normally closed safety switch operated by said safety switch actuator, and an enclosure temperature responsive switch being serially connected between said transformer secondary and said safety and ignition switch actuator circuits.

3. A control circuit for a fluid fuel burner for heating an enclosure of the type in which a main burner switch controls the flow of fuel to the burner and an ignition switch controls energization of the ignition means for the fuel, said circuit comprising: a transformer having a secondary winding serving as a source of power for the control circuit, a combustion responsive thermostat having an element adapted to respond to the heat of combustion at the burner and adapted to operate a first set of contacts which are closed in the absence of combustion at said burner and a second set of contacts which are closed in the presence of combustion at said burner, a safety switch actuator circuit and an ignition switch actuator circuit connected in parallel across said secondary winding and controlling energization of an electric safety switch actuator and an electric ignition switch actuator respectively, said safety switch actuator circuit comprising: serially connected a normally closed switch opened by said ignition switch actuator a predetermined time after its energization, a thermal electric safety switch actuator, and said first set of contacts of said combustion responsive thermostat; said ignition switch actuator circuit comprising: serially connected a normally open ignition switch actuator control switch, a thermal electric ignition switch actuator, and said second set of contacts of said combustion responsive thermostat; wiring means including a normally open safety switch actuator holding switch connecting an intermediate tap on said transformer secondary with said safety switch actuator circuit at the junction of said normally closed switch and said safety switch actuator; an electromagnetic main burner switch operator adapted when energized to close both said ignition switch actuator control switch and said safety switch actuator holding switch; said main burner switchoperator, a normally closed safety switch operated by saidsafety switch actuator, and an enclosuretem perature responsive switch being serially connected between said transformer secondary and said safety and ignition switch actuator circuits.

4. A control circuit for a fluid fuel burner for heating an enclosure of the type in which amainburner switch controls the flow of fuel to the burner and an ignition switch controls energization of the ignition means for the fuel, said circuit comprising: a transformer having a secondary winding serving as a source of power for the control circuit, a combustion responsive thermostat having an element adapted to respond to the heat of combustion at the burner and adapted to operate a first set of contacts which are closed in the absence of combustion at said burner and a second set of contacts which are closed in the presence of combustion at said burner, said element and said first and second set of. contacts being adapted for mounting remotely from the other circuit components, a safety switch actuator circuit and an ignition switch actuator circuit connected in parallel across said secondary winding and controlling energization of an electric safety switch actuator and an electric ignition switch actuator respectively, said safety switch actuator circuit comprising: serially connected a normally closed switch opened by said ignition switch actuator a predetermined time after its energization, a safety switch actuator, and said first set of contacts of said combustion responsive thermostat; said ignition switch actuator circuit comprising: serially connected a normally open ignition switch actuator control switch, an ignition switch actuator, and said second set of contacts of said combustion responsive thermostat; wiring means including a normally open safety switch actuator holding switch connecting an intermediate tap on said transformer secondary with said safety switch actuator circuit at the junction of said normally closed switch and said safety switch actuator; an electrical main burner switch operator adapted when energized. to close both said ignition switch actuator control switch and said safety switch actuator holding switch; said main burner switch operator, a normally closed safety switch operated by said safety switch actuator, and an enclosure temperature responsive switch being serially connected between said transformer secondary and said safety and ignition switch actuator circuits.

5. A control circuit for a fluid fuel burner for heating an enclosure of the type in which a main burner switch controls the flow of fuel to the burner and an ignition switch controls energization of the ignition means for the fuel, said circuit comprsing: a transformer having a secondary winding serving as a source of power for the control circuit, a combustion responsive thermostat having an element adapted to respond to the heat of combustion at the burner and adapted to operate a first set of contacts which are closed in the absence of combustion at said burner and a second set of contacts which are closed in the presence of combustion at said burner, said element and said first and second sets of contacts being adapted for mounting remotely from the other circuit components, a safety switch actuator circuit and an ignition switch actuator circuit connected in parallel across said secondary winding and controlling energization of an electric safety switch actuator and an electric ignition switch actuator respectively, said safety switch actuator circuit comprising: serially connected a normally closed switch opened by said ignition switch actuator a predetermined time after its energization, a thermal electric safety switch actuator, and said first set of contacts of said combustion responsive thermostat; said ignition switch actuator circuit comprising: serially connected a normally open ignition switch actuator control switch, a thermal electric ignition switch actuator, and said second set of contacts of said combustion responsive thermostat; wiring means including a normally open 7 (3 saietyqswitchnactuator holdingsswitch .connecting -an'interr serially connected between said transformer secondaryand mediate: tap; on said: transformer secondary-with: said saidisafety and ignitionswitch actuator circuits. safetyyswitchsactuator; circuit atthe: junctionuof said: norv mally; closedw switch; andjsaid safety: switch actuator; an References Clted lnflle of thls Patent electromagnetic main burner switch operator adapted 5 UNITED STATES PATENTS whemenergizedlo closeboth said 'ignitionswitch actuar torbcoutrol svyitch and said safety switch actuatorholdgzggg 'g 33 g; mgyswltch; sald mam burner swltch operator, anormally 2,743,768 Schell M y 1; 1956 closed safety'switch operated by said1safety switch actuaw tor; andan enclosure temperature responsive'switch being 10 

